1. Field of the Invention
The present invention relates to an optical module comprising an optical device which is a light-receiving device or light-emitting device.
2. Related Background Art
Optical modules such as receiving modules and transmitting modules are used in optical communication systems such as optical data links, optical LAN, and the like. A receiving module is equipped with a light-receiving device, for converting an optical signal transmitted through an optical fiber into an electric signal and outputting thus obtained electric signal; and a transmitting module is equipped with a light-emitting device, for converting an electric signal into an optical signal and sending out thus obtained optical signal to an optical fiber. Conventional examples of such optical modules are disclosed in Japanese Utility Model Application Laid-Open No. HEI 2-126107 and Japanese Patent Application Laid-Open No. HEI 2-278212.
An optical module comprises an optical device which is a light-receiving device or light-emitting device, and an electronic circuit connected to the optical device. In a conventional optical module, electronic components and wiring patterns constituting the electronic circuit are formed on a substrate or an island portion (substrate portion) of a lead frame functioning as a substrate, whereas the wiring pattern on the substrate and lead pins are connected to each other by wire bonding. Also, the electronic circuit and substrate, and individual components such as a metal package including an optical device are integrally molded with an insulating molding resin, so as to construct the optical module.
In the above-mentioned optical module, however, since the electronic circuit on the substrate and the lead frame are connected by wire bonding, it is necessary to provide the periphery of the substrate for wire bonding. Therefore, the size of the wiring substrate is restricted because of the necessity of the periphery region.
On the other hand, there has been known an optical module in which a lead frame is provided with an optical device mounting section and an electronic circuit mounting section which contain an optical device and an electronic circuit thereon respectively, and separately molded with a transparent resin (Proceedings of 48th Electronic Components & Technology Conference (1998), p. 1199). According to such a structure, the optical device and the electronic circuit are collectively mounted on the same lead frame.
In the structure mentioned above, the lead frame is formed by such a method as etching a sheet material or punching it with a pressing machine, whereby the wiring pattern of the electronic circuit is formed as well. Since the lead frame is formed from a single sheet material as such, however, cross wiring by which two or more wires are crossed cannot be made, whereby the degree of freedom in the electronic circuit configuration would be limited. For this matter, cross wiring may be realized by carrying out wire bonding in a part where crossing is necessary. In this case, however, impedance mismatching may occur, thus deteriorating circuit characteristics of the electronic circuit.
Also, in the case where a wiring pattern is formed by a lead frame, outer lead pins are formed simultaneously, whereby it is hard to form a wiring pattern with a wiring pitch not greater than the sheet thickness of the lead frame (on the order of 0.2 to 0.25 mm) due to conditions such as the strength of the lead frame and the easiness in its handling. Consequently, this technique cannot be utilized for forming complicated electronic circuits.